Relationchip between behaviors and plasma cortisol concentration during grouping of unfamiliar piglets

This study was carried out to clarify the stressors occurring during grouping of unfamiliar piglets. Twenty eight piglets from 6 litters, 65 +- 0 d old, (Landrace x Large White) x Duroc piglets were used. In experiment 1, 8 littermates x 1 litter and 4 littermates x 2 litters were used. Four piglets from a litter (moved-pigs A) and 4 piglets (moved-pigs B) from 8 littermates were respectively moved to each of two new pens, and the remaining k4 piglets from 8 littermates were not moved and housed in their own pen (rested-pigs). The other 4 littermates were not moved and used as control pigs. In experiment 2, 4 littermates x 3 litters were used. Four littermates (side-housed pigs B) were moved to a new pen next to the pen where the other 4 littermates (side-housed pigs A) were housed. A fence made of iron bars divided the border between two pens where the side-housed pigs A or B. The remaining 4 littermates were not moved and used as control pigs. At 24 h after the initiation of experiment 2, the fence between pens ware removed and then side-housed pigs A and B were grouped (experiment 3). Four littermates used as control pigs in experiment 2, were also used as the control pigs in experiment 3. The behavior of piglets was observed during the first 25 min after the initiation of the experiments 1, 2 and 3. Blood was obtained from all piglets 30 min before and 25 min after the initiation of each experiment and the concentration of plasma cortisol was determined. The behavior observed using the first 25 min, form the initiation of experiment tot he time of sampling blood for the determination of plasma cortisol, was sniffing the floor and walls of new pens in the move-pigs A and B, and walking about and gathered in the rested-pigs in experiment 1, seeing side-housed pigs B in the side-housed pigs A and sniffing a new pen and seeing side-housed pigs A in the side-housed B in exp-2, and fighting among piglets in exp-3, respectively